The designated laboratories of the International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) Network have been integral to its success in defining the standards of care for HIV infected pregnant women, children and adolescents. IMPAACT laboratory studies have elucidated the pathogenesis of HIV transmission, improved strategies designed to interrupt mother-to-child transmission (MTCT), optimized HIV treatment even in the setting of multi-drug resistance, and enhanced the diagnosis, prevention and management of HIV-related complications. The laboratories have been leaders in the development and evaluation of assays for infant diagnosis, viral load monitoring, drug resistance, antiretroviral pharmacology, host genetics and the measurement of immune responses. These studies were performed within the constraints of the small blood volumes available from our study populations and internationally in resource-limited settings. Often new methodologies and novel approaches have been developed to accommodate the limited specimens available from infants, children and pregnant women. In addition, all laboratory studies were performed under a comprehensive Total Quality Management Program that assured the highest standards of laboratory testing. The IMPAACT Network Laboratory Center (LC) is led by Grace Aldrovandi MD, CM, who will work closely with the IMPAACT Leadership Group, the Laboratory Steering Committee and the External Advisory Board to support, synergize and enhance the IMPAACT scientific agenda. The LC has 2 overarching specific aims: (1) Provide laboratory-based scientific leadership, consultation and laboratory capacity, including the development and implementation of innovative assays and protocols to enhance IMPAACT's Research Agenda and seven scientific aims. (2) Provide the technical, regulatory and administrative infrastructure and oversight for all laboratory testing done in support of IMPAACT clinical trials.